This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-085422, filed Mar. 24, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a power semiconductor device and, in particular, to a voltage drive type power MOS field effect transistor (hereinafter referred to as a power MOSFET) used for a power supply.
The voltage drive type power MOSFET is generally used as a switch for motor driving. For example, a switch for a vehicle-mounted ABS (Anti-Lock Braking System) is its typical application.
In a pump motor drive circuit having the above-mentioned power MOSFET, a control IC is generally mounted to the gates of a plurality of such power MOSFETS to control their gate potential. There is sometimes a case where a control IC-built IPD (Intelligent Power Device) or IPM (Intelligent Power Module) is connected to the gate.
Conventionally, in such a circuit arrangement, if the control IC is destroyed for some reason or other or if any inconvenience arises, the gate potential of the MOSFET is brought to a not-fixed state (floating state) and this causes an incomplete ON state. The incomplete ON state is intended to mean that, of a plurality of FET segments, some segment is rendered ON and some segment is not rendered ON.
If these segments are brought to such states, the flow of electric current concentrates onto the ON-state segment, so that the ON-state segment becomes defective due to the occurrence of thermal destruction. If the ON-state segment is thermally destroyed and there occurs a short-circuited state, a full power is applied to a pump motor, thus causing a danger of the motor being destroyed.
Further, the destruction of this segment is less likely to occur in a normal temperature range and, usually, a constant unstable state is continued until a final destruction occurs. This problem should be solved, for example, in a vehicle-mounted application requiring a reliability under the normal and high temperatures.
It may be considered that the adoption of the IPD, IPM, etc., with a simple circuit incorporated therein be made as a solution to this problem.
If, however, the IPD, IPM, etc., are adopted, then a cost performance becomes worse.
The present invention has been achieved with the above-mentioned task in mind and it is accordingly the object of the present invention to provide a power MOSFET-equipped semiconductor device which, without using many component parts and without adopting an IPD, IPM, etc., involving a high cost, incorporates a circuit of a simpler arrangement therein and, by doing so, can prevent the power MOSFET from being thermally destroyed in the case where the gate potential of the power MOSFET is brought to a not-fixed state.
In order to achieve the above-mentioned object, a power semiconductor device according to a first aspect of the present invention comprises a voltage drive type power MOS transistor having a gate, source and drain; a series connection of a first resistor and Zener diode across which a drain-to-source voltage of the power MOS transistor is applied; a second resistor across which a gate-to-source voltage of the power MOS transistor is applied; and a series connection of a third resistor and MOS transistor across which the gate-to-source voltage of the power MOS transistor is applied, the MOS transistor having a gate, source and drain, and the gate of the MOS transistor being connected to a node between the first resistor and the Zener diode.
In order to achieve the above-mentioned object, a power semiconductor device according to a second aspect of the present invention comprises a voltage drive type power MOS transistor having a gate, source and drain and formed on a semiconductor substrate; a series connection of a first resistor and Zener diode across which a drain-to-source voltage of the power MOS transistor is applied, the first resistor and Zener diode being formed on the semiconductor substrate; a second resistor across which a gate-to-source voltage of the power MOS transistor is applied, the second resistor being formed on the semiconductor substrate; and a series connection of a third resistor and MOS transistor across which the gate-to-source voltage of the MOS transistor is applied, the MOS transistor having a gate, source and drain, the gate of the MOS transistor being connected to a node between the first resistor and the Zener diode, and the third resistor and MOS transistor being formed on the semiconductor substrate.
In the power semiconductor device thus structured, a variable resistance circuit is provided between the gate and the source of the power MOS transistor. The variable resistance circuit has the first resistor and Zener diode, second resistor, and third resistor and MOS transistor. By doing so it is possible to prevent a thermal destruction of the power MOS transistor which may occur in the case where the gate potential of the power MOS transistor is brought to a not-fixed state.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.